Reusing the 1-1/2" vent and connecting to the new waste line would be fine. The proper couplings will need to be used to transition between the pipes. As long as all of the pipe and fittings are plumbed to current plumbing codes, it will be fine. Pipes that are okay to use include, Copper, Steel, Cast-iron, ABS and PVC

: I am replacing my kitchen drain line over to the main stand. I am leaving the old pipes in the wall and running new PVC through the floor right from the sink.

: Question: I want to utilize the old vent. Does it matter at what point in the drain line that vent attaches?

: My idea that prompts this is to cap the old drain line at the wall under the sink, and where the new emerges under the rafters, tie in the old drain line to use as vent. Essentially the New drain and old Drain join at a level point and run horizontal across the floor until they reach the main stand.